The effects of intraventricular injections of norepinephrine (NE) and dopamine (DA) on physiological responses of single comb white Leghorn hens housed at ambient temperatures of g degrees C and 20 degrees C have been measured. Physiological responses which have been measured are: body, comb, skin and leg temperatures; heart and respiration rates; shivering; heat production (O2 and CO2 measurements); sensible heat loss (partitioned into convective and radiant); and evaporative heat loss. Injections of NE and DA were made in 4 birds at both 9 degrees or 20 degrees C. Two sham injections at 9 degrees C and 2 sham injections at 20 degrees C were made. Results show that both NE and DA injections caused decreases in body temperature, heart rate, respiration rate, heat production and heat loss at both ambient temperatures. Both comb and leg temperatures and sensible heat loss indicate initial vasodilation immediately after injection followed by vasoconstriction as body temperature fell. In birds at 9 degrees C shivering was inhibited after drug injections. Following the decrease in body temperature, shivering was again initiated with a simultaneous increase in body temperature to the normal level. At both ambient temperatures the changes (decreases) in all of the physiological responses were larger in magnitude for NE. Decreases after DA injections were also shorter in duration compared to changes after NE injections. Future work will be devoted to studies of physiological responses after injections of NE, DA and serotonin (5-HT) at 9 degrees C, 20 degrees C and 35 degrees C and to determining if these biogenic amines reflect a physiologic role in bird thermoregulation.